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When last seen Mr Casey was wearing a short-sleeved navy polo top with a grey collar and grey shoulders, light blue chinos and dark navy shoes.

Anyone with information is asked to contact Henry Street Garda Station on 061 212400.

Superintendent Daniel Keane said Mr Casey's disappearance is totally out of character.

"We are just anxious that people, our residents and businesses in the (Cornmarket) area would search their alley-ways, their sheds, just in case Mark went to sleep there or may have come across harm’s way.